Body-composition dynamics in meadow voles (Microtus pennsylvanicus) were examined by noninvasive EM-SCAN® methods for 12 mo. At the population level, body mass and fat-free mass varied seasonally with highs in spring and summer and lows in autumn and winter. In autumn and winter, losses in body mass and fat-free mass occurred in individual adults (40 g summer body mass), whereas voles maintained 2–3 g of lipid mass year-round, equating to 4% body fat in summer and 7% body fat in winter. Thus, changes in body composition were primarily due to changes in fat-free mass and not changes in lipid mass. Voles may rely more on energy sparing (reduction in fat-free mass and body mass) than on energy storing as a primary means of overwinter survival. Compared with results from more northern populations of arvicoline rodents, the lesser change in total body mass observed in this study suggests a latitudinal influence on seasonal change, possibly due to reduced environmental circumstances.
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Vol. 149 • No. 1